1. Field
The present disclosure relates to a fuel cell stack.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell includes a membrane electrode assembly (MEA), in which an anode electrode is disposed on one side of a solid-polymer electrolyte membrane and a cathode electrode is disposed on the other side of the solid-polymer electrolyte membrane. The solid-polymer electrolyte membrane is made from a polymer ion-exchange membrane. The MEA and a pair of separators, sandwiching the MEA therebetween, constitute a power generation cell (unit cell). Several tens to several hundreds of such power generation cells are stacked and used, for example, as a vehicle fuel cell stack.
A fuel cell usually has a so-called internal manifold structure for supplying a fuel gas and an oxidant gas, each of which is a reactant gas, respectively to anode electrodes and cathode electrodes of power generation cells that are stacked. The internal manifold structure includes a reactant gas inlet manifold and a reactant gas outlet manifold, each extending through the power generation cells in a direction in which the power generation cells are stacked. The reactant gas inlet manifold and the reactant gas outlet manifold (hereinafter, each of which may be referred to as a reactant gas manifold) are respectively connected to an inlet and an outlet of a reactant gas channel, through which the reactant gas is supplied along an electrode surface.
In this case, the reactant gas manifold has a comparatively small opening area. Accordingly, in order to allow the reactant gas to smoothly flow through the reactant gas channel, it is necessary to provide buffer portions (an inlet buffer portion and an outlet buffer portion), for diffusing the reactant gas, near the reactant gas manifold.
For example, Japanese Patent No. 5128861 describes a fuel cell in which the size of a buffer portion is reduced as much as possible and with which a desirable power generation performance can be obtained with a lightweight and compact structure.
In this fuel cell, a separator includes an inlet buffer portion, which is substantially triangular and is located near an inlet of a reactant gas channel, and an outlet buffer portion, which is substantially triangular and is located near an outlet of the reactant gas channel. The average pressure losses of the inlet buffer portion and the outlet buffer portion are each lower than or equal to the average pressure loss of the reactant gas channel. Accordingly, the flow rate of a reactant gas through the reactant gas channel can be made uniform, and it is possible to uniformly supply the reactant gas from a reactant gas manifold to the entire surface of the reactant gas channel.